#include <fstream>
#include <bitset>

using namespace std;
bitset <2000002> a;
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, k, i, j;
    fin >> n;
    for (i=4; i<=n; i=i+2)
        a[i]=1;
    for (i=3; i*i<=n; i=i+2)
        if (a[i]==0)
            for (j=i*i; j<=n; j=j+2*i)
                a[j]=1;
    k=1;
    for (i=3; i<=n; i=i+2)
    {
        if (a[i]==0) k++;
    }




    fin.close();
    fout.close();
    return 0;
}